1. Field of the Invention
The present invention relates to a driving unit and a battery-assisted bicycle that assists a rider's pedaling effort with a driving force from an electric motor.
2. Description of the Related Art
There has been a known battery-assisted bicycle that detects a torque generated at a crankshaft rotated together with pedals by a torque detector and controls an electric motor based on a detection result in order to assist the rider's pedaling effort. Such a battery-assisted bicycle switches between on and off of assist control in response to a torque generated at the crankshaft when a rider pushes on the pedals, for example, as disclosed in Japanese Patent No. 4129084.
More specifically, according to the disclosure in Japanese Patent No. 4129084, if a torque generated at the crankshaft is not less than an assist restarting determination value in an assist stopped state, assist control is started. On the other hand, according to the disclosure in Japanese Patent No. 4129084, assist control is stopped if a torque continues to be not more than an assist cut determination value in an assisted state at least for a determination duration.
In recent years, battery-assisted bicycles adapted to assist a rider's pedaling effort in a higher assist ratio have been requested. In such a battery-assisted bicycle, auxiliary motive power by an electric motor is larger than the rider's pedaling effort. More specifically, as the assist ratio increases, the pedaling effort by the rider decreases.
Therefore, if starting/stopping of assist control is determined using a torque generated at the crankshaft as disclosed in Japanese Patent No. 4129084, a battery-assisted bicycle with a high assist ratio ends up repeatedly starting and stopping assist control in response to slight changes of a small torque value.
More specifically, in the structure disclosed above, the assist control starts or stops in response to a slight change in the torque value, and the rider may feel uncomfortable.